Apparatus for mitigation of thermal event propagation for battery systems

ABSTRACT

Apparatus for mitigating propagation of thermal events between battery cells within a battery module assembly (10) is provided. The apparatus comprises one or more of several features that function to prevent a runaway thermal event within one battery cell (48) from triggering a fire or other thermal event within another battery cell within the battery module assembly (10). The apparatus may comprise one or more of: (i) a compressive wrap (88) applied to a battery cell (48); (ii) a layered barrier material (104) positioned between adjacent battery cells (48); (iii) silicone rubber supports (94) positioned adjacent the battery terminals (62, 64), (iv) a light-weight, fire-resistant housing composite panel, and (v) rupturable diaphragms (36) configured to vent gases and ejecta from a battery cell undergoing a thermal event.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention is generally directed toward apparatus formitigating propagation of thermal events between battery cells within abattery module assembly. The thermal events, which originate within oneof the battery cells, may include the discharge of flames, heat andejecta from a battery cell, and can create a serious risk of initiatinga similar thermal event in an adjacent battery cell within the samebattery module or other battery modules within the same battery system.The mitigating apparatus provides passive protection for battery systemsand serves as a failsafe mechanism for other, active protection systemsthat may be provided as a part of the overall battery system.

Description of the Prior Art

The demand for alternative, environmentally-friendly sources of poweringmachines and equipment continues to surge. In particular, demand hasgrown for machines that rely upon battery systems to provide power fortheir operation as opposed to more conventional means of powergeneration, such as through burning of fossil fuels. While the rise inpopularity of electric cars and other machines conventionally powered byinternal-combustion engines is manifest, many other types of vehiclesthat already use electric propulsion systems continue to rely uponfossil-fuel powered generators in order to provide the electricityneeded for their propulsion and other operational systems. Thesevehicles include cargo ships, ferries, aircraft, mining equipment,aviation ground service equipment, hyperloop pods, and locomotives.Aside from transportation applications, battery-powered electricalsystems can find use in many off-grid applications that presently relyupon either fossil fuel power generation, or less-consistent sources ofclean energy such as solar and wind.

Lithium ion battery cells are presently preferred for many power storageapplications. However, safety concerns associated with the use of thesecells is well-known and steps must be taken to ensure safe operation oflarge-scale battery systems employing lithium ion battery cells. Oneparticular operational safety concern associated with lithium ionbattery cell usage is thermal energy management. Lithium ion cells tendto release significant quantities of heat during normal cell operation.The generation of this heat needs to be managed, and the system designshould account for adequate cooling and/or heat dissipation so that thebattery cells can operate efficiently and safely. If a battery celloverheats, a runaway chemical reaction within the battery cell canresult, sometimes with very serious consequences. For instance, arunaway cell can explode, catch fire, and/or eject hot gases or materialtherefrom. The hot ejecta, gas, and flame can then be spread to adjacentbattery cells and cause further runaway cells thereby exacerbating analready serious condition.

Lithium ion battery systems are often equipped with several activemonitoring and mitigation systems that continuously monitor a host ofparameters associated with battery system operation and are operable totake steps to detect signs of the beginning of an untoward thermal eventand mitigate it before it becomes a problem. Such mitigating stepsinclude taking the cell in question offline, activating fire suppressingsystems, and/or alerting service technicians to inspect the cell ormodule in question. However, some industry regulatory authoritiesrequire that passive back-up or fail safe systems be provided in casethe active mitigation systems fail or become disabled. The NorwegianMaritime Authority is one such regulatory body that requires thepresence of a passive protection system for all battery-powered andhybrid vessels operating in its waters.

Thus, a need exists for apparatus that can be used with battery systemsto provide for protection from and prevent propagation of thermal eventsassociated with battery cells contained therein.

SUMMARY OF THE INVENTION

According to one embodiment of the present invention there is provided aprismatic battery cell that comprises a compressive wrap disposed aroundat least a portion of the outer cell case within which the contents ofthe battery cell are contained. The compressive wrap is operable toconstrain hoop stresses acting upon the cell case during thermalexpansion of the cell. In preferred embodiments, the outer cell casepresents a pair of opposed, generally planar surfaces interconnected byopposed sidewall segment pairs. The compressive wrap is disposed aroundthe cell case in covering relationship to at least a portion of theplanar surfaces and at least a portion of one of the sidewall segmentpairs. In particularly preferred embodiments, there is at least onesidewall segment of one of the sidewall segment pairs that is uncoveredby the compressive wrap and configured to create at least onepredetermined point of cell case failure during a thermal event in thecell through which ejecta, gas, and or flames are released from thecell.

According to another embodiment of the present invention there isprovided a method of constraining a prismatic battery cell comprising acell case in which the contents of the battery cell are contained. Inpreferred embodiments, the cell case presents a pair of opposed,generally planar surfaces interconnected by opposed sidewall segmentpairs. The method comprises applying a compressive wrap to the cellcase. In particularly preferred embodiments, the compressive wrap isapplied in covering relationship to at least a portion of the planarsurfaces and a least a portion of one of the sidewall segment pairs.Generally, the compressive wrap functions to constrain hoop stressesacting upon the cell case during thermal expansion of the cell. Inpreferred embodiments, at least one sidewall segment of one of thesidewall segment pairs is left uncovered by the compressive wrap therebycreating at least one predetermined point of cell case failure during athermal event in the cell through which ejecta, gas, and/or flames arereleased from the cell.

According to another embodiment of the present invention there isprovided a prismatic battery cell comprising an outer cell case in whichthe contents of the battery cell are contained. The cell case presents apair of opposed, generally planar surfaces interconnected by opposedsidewall segment pairs. There is at least one cell flange extending fromone or more of the sidewall segments. At least two terminals extend fromone or more of the sidewall segments. The at least two terminals are atleast partially surrounded by the at least one cell flange. There is atleast one pliable, temperature-resistant strip of material disposed onat least one side of and overlying the at least one cell flange.

According to another embodiment of the present invention there isprovided a method of protecting a battery cell from physical and thermaldamage. The battery cell comprises an outer cell case in which thecontents of the battery cell are contained. The cell case presents apair of opposed, generally planar surfaces interconnected by opposedsidewall segment pairs. At least one cell flange extends from one ormore of the sidewall segments. At least two terminals extend from one ormore of the sidewall segments. The at least two terminals are at leastpartially surrounded by the at least one cell flange. The methodcomprises placing at least one pliable, temperature-resistant strip ofmaterial on at least one side of and overlying the at least one cellflange.

According to another embodiment of the present invention there isprovided a battery module assembly. In preferred embodiments, thebattery module assembly comprises at least two battery cells and one ormore of the following:

-   -   (i) a layered barrier material disposed between the at least two        battery cells configured to thermally isolate and control,        prevent, or mitigate cell-to-cell propagation of a thermal event        occurring within at least one of the battery cells;    -   (ii) a battery module housing configured to house a plurality of        battery cells and comprising at least one composite panel        comprising an outboard metallic layer, an inboard layer of an        FR4-rated sheet material, and at least one graphitic carbon        sheet positioned therebetween;    -   (iii) one or more busbars operable to connect the at least two        battery cells located within a battery module housing, and one        or more busbar shields configured to at least partially cover        the one or more busbars and shield electrical components located        outboard of the one or more busbars and within a passage of the        housing from contacting the one or more busbars during a thermal        event associated with one or more of the plurality of battery        cells; and    -   (iv) a battery module housing comprising a passage within the        housing and at least one outlet interconnecting the passage and        the environment outside of the housing, there being a rupturable        diaphragm normally covering the passage and blocking        communication between the passage and the environment outside        the housing.

In preferred embodiments of the present invention, the layered barriermaterial includes at least two sheets of an anisotropic material. Atleast one of the sheets of anisotropic material is in direct facingcontact with one of the at least two battery cells, and at least oneother of the sheets of anisotropic material is in direct facing contactwith one other of the at least two battery cells. The at least twosheets of anisotropic material have a high thermal conductivity in thein-plane direction and are operable to direct thermal energy away from asurface of the cell with which the sheet is in contact. The at least twosheets of anisotropic material are operable to prevent and/or retardpenetration of a flame originating from the battery cell with which itis in contact in a direction toward the at least one other battery cell.The layered barrier material optionally includes at least one sheet, andpreferably at least two sheets, of a thermal insulation material havinghigh thermal resistance. When at least two sheets of the thermalinsulation material are present, one of the at least two sheets ofthermal insulation material is positioned in direct facing contact withone of the at least two sheets of anisotropic material and the other ofthe at least two sheets of thermal insulation material is positioned indirect facing contact with the other of the at least two sheets ofanisotropic material. The at least two sheets of thermal insulationmaterial are operable to retard and/or impede the flow of heatoriginating within one of the battery cells in a direction toward the atleast one other battery cell. The layered barrier material furtherincludes a compliant material positioned between the at least two sheetsof anisotropic material and optional thermal insulation material undercompression. The compliant material is operable for maintaining the atleast two sheets of anisotropic material in direct facing contact withthe at least two battery cells regardless of thermally-induced changesin volume that the at least two battery cells may experience duringnormal cell operation.

In preferred embodiments of the present invention, the outboard metalliclayer of the battery module housing composite panel comprises aluminum,and the FR4-rated sheet material comprises a woven fiberglass and epoxyresin laminate material. The composite panel defines, at least in part,a passageway configured to conduct a flow of ejecta and gas from athermal event associated with one or more battery cells within thebattery module housing toward an outlet formed in the housing.

In preferred embodiments of the present invention, the busbar shieldscomprise an FR4-rated sheet material, and more preferably a wovenfiberglass and epoxy resin laminate material. The busbar shields operateto prevent wiring running within a passage of the housing whoseinsulation may have become damaged as a result of a thermal eventassociated with one or more of the battery cells, from contacting one ofthe busbars and causing a short circuit.

According to another embodiment of the present invention there isprovided a battery module assembly. The battery module assemblycomprises a battery module housing configured to house a plurality ofprismatic battery cells. One or more of the prismatic battery cellscomprises an outer cell case in which the contents of the battery cellare contained. The cell case presents a pair of opposed, generallyplanar surfaces interconnected by opposed sidewall segment pairs. Acompressive wrap is disposed around the cell case in coveringrelationship to at least a portion of the planar surfaces and at least aportion of one of the sidewall segment pairs. The compressive wrap isoperable to constrain hoop stresses acting upon the cell case duringthermal expansion of the cell. There is at least one sidewall segment ofone of the sidewall segment pairs that is uncovered by the compressivewrap and is configured to create at least one predetermined point ofcell case failure during a thermal event in the cell through whichejecta, gas, and/or flames are released from the cell. The batterymodule assembly further comprises a layered barrier material disposed inbetween at least two of the plurality of prismatic battery cells. Thelayered barrier material is configured to thermally isolate and controlor prevent cell-to-cell propagation of a thermal event occurring withinat least one of the battery cells. The layered barrier materialcomprises at least two sheets of an anisotropic material. At least oneof the sheets of anisotropic material is in direct facing contact withone of the at least two battery cells. At least one other of the sheetsof anisotropic material is in direct facing contact with one other ofthe at least two battery cells. The layered barrier material optionallycomprises at least one, and preferably two, sheets of a thermalinsulation material. When two sheets of the thermal insulation materialare used, one of the at least two sheets of thermal insulation materialis positioned in direct facing contact with one of the at least twosheets of anisotropic material, and the other of the at least two sheetsof thermal insulation material is positioned in direct facing contactwith the other of the at least two sheets of anisotropic material. Thelayered barrier material further comprises a compliant materialpositioned between the at least two sheets of anisotropic material andoptional thermal insulation material under compression. The compliantmaterial is operable for maintaining the at least two sheets ofanisotropic material in direct facing contact with the at least twobattery cells.

According to another embodiment of the present invention there isprovided a battery module assembly comprising a battery module housingconfigured to house a plurality of prismatic battery cells. One or moreof the prismatic battery cells comprises an outer cell case in which thecontents of the battery cell are contained. The cell case presents apair of opposed, generally planar surfaces interconnected by opposedsidewall segment pairs. A compressive wrap is disposed around the cellcase in covering relationship to at least a portion of the planarsurfaces and at least a portion of one of the sidewall segment pairs.The compressive wrap is operable to constrain hoop stresses acting uponthe cell case during thermal expansion of the cell. There is at leastone sidewall segment of one of the sidewall segment pairs that isuncovered by the compressive wrap and is configured to create at leastone predetermined point of cell case failure during a thermal event inthe cell through which ejecta and gas are released from the cell. Theone or more battery cells comprises at least one cell flange extendingfrom one or more of the sidewall segments and at least two terminalsextending from one or more of the sidewall segments. The at least twoterminals are at least partially surrounded by the at least one cellflange. There is at least one pliable, temperature-resistant strip ofmaterial disposed on at least one side of and overlying the at least onecell flange.

According to another embodiment of the present invention there isprovided a battery module assembly comprising a battery module housingconfigured to house a plurality of battery cells and a layered barriermaterial disposed in between at least two of the plurality of batterycells. The layered barrier material is configured to thermally isolateand control or prevent cell-to-cell propagation of a thermal eventoccurring within at least one of the battery cells. The layered barriermaterial is configured to thermally isolate and control or preventcell-to-cell propagation of a thermal event occurring within at leastone of the battery cells. The layered barrier material comprises atleast two sheets of an anisotropic material. At least one of the sheetsof anisotropic material is in direct facing contact with one of the atleast two battery cells. At least one other of the sheets of anisotropicmaterial is in direct facing contact with one other of the at least twobattery cells. The layered barrier material further comprises at leasttwo sheets of a thermal insulation material. One of the at least twosheets of thermal insulation material is positioned in direct facingcontact with one of the at least two sheets of anisotropic material, andthe other of the at least two sheets of thermal insulation material ispositioned in direct facing contact with the other of the at least twosheets of anisotropic material. The layered barrier material furthercomprises a compliant material positioned between the at least twosheets of thermal insulation material under compression. The compliantmaterial is operable for maintaining the at least two sheets ofanisotropic material in direct facing contact with the at least twobattery cells. Each of the plurality of battery cells comprises an outercell case in which the contents of the battery cell are contained. Thecell case presents a pair of opposed, generally planar surfacesinterconnected by opposed sidewall segment pairs. At least one cellflange extends from one or more of the sidewall segments. At least twoterminals extend from one or more of the sidewall segments. The at leasttwo terminals are at least partially surrounded by the at least one cellflange. There is at least one pliable, temperature-resistant strip ofmaterial disposed on at least one side of and overlying the at least onecell flange.

According to another embodiment of the present invention there isprovided a battery module assembly comprising a battery module housingconfigured to house a plurality of prismatic battery cells. One or moreof the prismatic battery cells comprise an outer cell case in which thecontents of the battery cell are contained. The cell case presents apair of opposed, generally planar surfaces interconnected by opposedsidewall segment pairs. The one or more prismatic battery cells furthercomprise a compressive wrap disposed around the cell case in coveringrelationship to at least a portion of the planar surfaces and at least aportion of one of the sidewall segment pairs. The compressive wrap isoperable to constrain hoop stresses acting upon the cell case duringthermal expansion of the cell. There is at least one sidewall segment ofone of the sidewall segment pairs that is uncovered by the compressivewrap and configured to create at least one predetermined point of cellcase failure during a thermal event in the cell through which ejecta andgas are released from the cell. The battery module housing comprises atleast one composite panel comprising an outboard metallic layer, aninboard layer of an FR4-rated sheet material, and at least one graphiticcarbon sheet positioned therebetween. The composite panel defines atleast in part a passageway configured to conduct a flow of ejecta andgas from a thermal event associated with one or more battery cellswithin the battery module housing toward an outlet formed in thehousing.

According to another embodiment of the present invention there isprovided a battery system comprising a plurality of any of the batterymodules described herein.

According to another embodiment of the present invention there isprovided a vehicle comprising one or more of the prismatic battery cellsor battery modules, or battery systems described herein. In preferredembodiments, the vehicle is a marine vessel, such as a ship or boat.

According to an embodiment of the present invention, a method ofthermally isolating battery cells within a battery module assemblycomprising at least two battery cells is provided. The method comprisespositioning a layered barrier material in between the at least twobattery cells. The layered barrier material is configured to thermallyisolate and control or prevent cell-to-cell propagation of a thermalevent occurring within at least one of the battery cells. Thepositioning of the layered barrier material comprises placing a firstsheet of anisotropic material in direct facing contact with one of theat least two battery cells. The anisotropic material has a high thermalconductivity in the in-plane direction and is operable to direct thermalenergy away from a surface of the cell with which the sheet is incontact. The anisotropic material is operable to prevent and/or retardpenetration of a flame originating from the battery cell with which itis in contact in a direction toward the at least one other battery cell.Optionally, a first sheet of a thermal insulation material having a highthermal resistance is placed in direct facing contact with the firstsheet of anisotropic material. The thermal insulation material isoperable to retard and/or impede the flow of heat originating within oneof the battery cells in a direction toward the at least one otherbattery cell. A second sheet of the anisotropic material is placed indirect facing contact with the other of the at least two battery cells.Optionally, a second sheet of the thermal insulation material is placedin direct facing contact with the second sheet of anisotropic material.A compliant material is positioned between the first and second sheetsof anisotropic material and optional thermal insulation material andmaintained under compression therebetween. The compliant materialmaintains the at least two sheets of anisotropic material in directfacing contact with the at least two battery cells regardless ofthermally-induced changes in volume that the at least two battery cellsmay experience during normal cell operation.

According to an embodiment of the present invention, a battery moduleassembly is provided that comprises a battery module housing, aplurality of battery cells located within the battery module housing,and a layered barrier material in contact with adjacent battery celled.The battery module housing has a longitudinal axis that extends thelength of the battery module housing and a transverse axis that isnormal to the longitudinal axis. The layered barrier material comprisesat least two sheets of anisotropic material. At least one of the sheetsof anisotropic material is in direct facing contact with one of thebattery cells, and at least one other of the sheets of anisotropicmaterial is in direct facing contact with at least one other of thebattery cells. The battery module housing is configured to apply acompressive force to the plurality of battery cells in a directionparallel to the transverse axis. A compressive force also is applied tothe plurality of battery cells in a in a direction that is parallel tothe longitudinal axis.

According to an embodiment of the present invention, a battery moduleassembly is provided that comprises a battery module housing, aplurality of battery cells located within the battery module housing,and at least one passageway located between the battery module housingand the plurality of battery cells. The at least one passageway isconfigured to conduct a flow of ejecta and gas from a thermal eventassociated with one or more battery cells within the battery modulehousing toward an outlet formed in the housing. The outlet is coveredwith a rupturable diaphragm configured to open in response to thethermal event and permit communication between the passageway and theexterior of the housing. The rupturable diaphragm also is configured toresist opening due to a thermal event that is external to the housing.

According to an embodiment of the present invention, a prismatic batterycell assembly is provided that comprises an outer cell case, at leastone cell flange, at least two terminals, and a bead of a pliable,temperature-resistant material disposed about the periphery of the cellcase. The cell case has a pair of opposed, generally planar surfacesinterconnected by opposed sidewall segment pairs. The at least one cellflange extends from one or more of the sidewall segments. The at leasttwo terminals extend from one of the sidewall segments and are at leastpartially surrounded by the at least one cell flange. The bead of apliable, temperature-resistant material is disposed about a majority ofthe periphery of the sidewall segments and overlies at least a portionof the at least one cell flange. The bead is operable to apply acompressive force to the outer cell case.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a battery module assembly according tothe present invention illustrating the end of the assembly comprisingrupturable diaphragms covering the battery module housing outlets;

FIG. 2 is an isometric view of the battery module assembly illustratingthe end of the assembly comprising various electrical connectors;

FIG. 3 is a broken cross-sectional view of the battery module assemblywith a portion of the assembly removed for ease of illustration;

FIG. 4 is an isometric, sectioned view of the battery module assemblyillustrating the stack of battery cells contained within the batterymodule housing;

FIG. 5 is an expanded view of a stack of battery cell units containedwith the battery module housing;

FIG. 6 is an expanded view of a battery cell in accordance with oneembodiment of the present invention;

FIG. 7 is an isometric end view of the fully-assembled battery cell; and

FIG. 8 is an expanded view of another embodiment of a stack of batterycell units included within a battery module assembly

While the drawings do not necessarily provide exact dimensions ortolerances for the illustrated components or structures, the drawingsare to scale with respect to the relationships between the components ofthe structures illustrated in the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Definitions

As used herein, the term “battery cell” refers to an electrochemicalcell that can generate electrical energy from a chemical reaction. Thebattery cell may be an electrolytic cell in which a cathode and anodeare separated by an electrolyte. An exemplary battery cell for use withthe present invention is a lithium ion battery cell. There are manytypes of electrolytes that may be used in lithium ion battery cellsincluding, but not limited to mixtures of organic carbonates such asethylene carbonate or diethyl carbonate containing complexes of lithiumions. These non-aqueous electrolytes generally use non-coordinatinganion salts such as lithium hexafluorophosphate (LiPF₆), lithiumhexafluoroarsenate monohydrate (LiAsF₆), lithium perchlorate (LiClO₄),lithium tetrafluoroborate (LiBF₄), and lithium triflate (LiCF₃SO₃). Itis noted that many concepts of the present invention described hereincan also be applicable to other electrochemical devices and energystorage devices besides those based upon battery cells, includinglithium ion capacitors and supercapacitors. For expediency purposes, allsuch non-battery devices are encompassed by the term “battery cell” asused herein.

As used herein, the term “battery module” refers to a collection of twoor more battery cells. The battery cells within the battery module maybe connected in series, in parallel, or there may be cells connected inseries and cells connected in parallel within the same module.

As used herein, the term “battery system” refers to a collection of twoor more battery modules.

As used herein, the term “FR4-rated” refers to a National ElectricalManufacturers Association (NEMA) grade designation for certain compositematerials, especially glass-reinforced epoxy laminate materials that areflame retardant.

As used herein, the term “graphitic carbon” refers to allotropes ofcarbon having graphene as a basic structural element including, but notlimited to, graphite, charcoal, carbon nanotubes, and fullerene.

As used herein, the term “runaway event” means an uncontrolledexothermic chemical reaction occurring within a battery cell that mayresult in the release of heat, flame, gases, and/or other particulatematter (i.e., ejecta) from the cell. A runaway event is generallyconsidered an extremely hazardous condition and one that may result in afire that could potentially propagate to other battery cells within thevicinity of the cell in which the event originates.

Turning now to FIGS. 1 and 2, an exemplary battery module assembly 10according to one embodiment of the present invention is illustrated.Battery module assembly 10 generally comprises a battery module housing12, which encloses a plurality of battery cells and other associatedcomponents therein, which are described in greater detail below. Asillustrated, housing 12 is rectangular in shape, although this need notalways be the case, and is comprised of six assembled panels. Panels 14and 16 are generally the largest panels and are positioned opposite eachother. One or more of panels 14, 16 may comprise a heat transfer surface18, the function of which is described in greater detail below.

Housing 12 further comprises an opposed pair of composite side panels28, 30. The construction of side panels 28, 30 is described in furtherdetail below. Side panels 28, 30 interconnect panels 14, 16 alonglongitudinally extending side margins thereof. End panels 32, 34 arepositioned transversely to side panels 28, 30 and effectively serve asend caps of housing 12. It is observed that end panel 32 may be equippedwith rupturable diaphragms 36, whose function is explained below. Endpanel 34 may comprise various electrical connectors to which power leads(not shown) and monitoring and control systems (not shown) may beattached to the battery module 10.

One or more of the panels making up housing 12, and in particular panels14, 16, 28, and 30, may comprise a light-weight metal, such as aluminum,to reduce the overall weight of the housing. However, other metals, suchas steel, can be used. In certain embodiments, panels 14, 16, 28, and 30comprise a lightweight, high-strength material such as aluminum orcarbon fiber.

In certain embodiments, it is preferable, that once all panels areassembled, housing 12 forms a generally water-tight structure thatprevents, or at least minimizes, entry of moisture, dust, and/or otherforeign matter into the interior of the housing. Likewise, and except asexplained below with reference to diaphragms 36, housing 12 alsoprevents material associated with or generated from the battery cellslocated within the housing from escaping in an uncontrolled manner.Housing 12 further comprises a plurality of strap members 20 disposedcircumferentially about panels 14, 16, 28, and 30. The function of strapmembers 20 is described in greater detail below; however, generallystrap members 20 provide a compressive force to the panels they contact,and in particular panels 14 and 16. Strap members 20 are preferably madefrom steel, but any suitable material may be used.

A plurality of battery modules 10 may be assembled together into abattery system that is sized to meet the needs of a particularapplication. The battery system may include racks or shelving units (notshown) onto which the battery modules 10 may be secured. Battery modules10 can be connected in series and/or in parallel within the overallbattery system as the needs of the particular application require.

FIG. 3 illustrates composite side panels 28, 30 in greater detail. Thesepanels are configured to provide enhanced protection against thermalevents originating within a battery cell contained within housing 12. Asexplained in greater detail below, the battery cells are speciallyconfigured to vent flame, gas, and other ejecta in a direction toward atleast one of side panels 28, 30 should the cell experience a runawaythermal event. Conventionally, panels exposed to such conditions wereconstructed of single-material sheets, such as steel, that couldwithstand the high-temperatures associated with these types of thermalevents. However, in some applications, such materials are impractical asthey add considerable weight to the battery module housing. Accordingly,in certain embodiments of the present invention, side panels 28, 30 areconstructed of a composite material that is much lighter in weight butpossesses adequate heat-resistant characteristics for use as a housingpanel.

Composite side panels 28, 30 comprise an outboard metallic ornon-metallic structural layer 38, an inboard layer 40, and at least onegraphitic carbon sheet 42 positioned therebetween. Preferably, panels28, 30 comprise a plurality of graphitic carbon sheets stacked 42together. In preferred embodiments, the FR4-rated sheet materialcomprises a woven fiberglass and epoxy resin laminate material. Inparticularly preferred embodiments, the FR4-rated material comprises aGarolite material having a tensile strength of 241-345 MPa, an impactstrength of 30-65.4 kg-cm/cm, a Rockwell hardness of M100 to M110, and athickness of 0.127 mm to 2.54 cm.

The FR-4 rated sheet material serves as a flame barrier that preventspenetration of flames being ejected by a battery cell within the batterymodule 10. The graphitic carbon sheet or sheets provide a thermalbarrier to protect the outboard metallic layer 38 from temperatures thatcould cause it to melt. The graphitic carbon sheets advantageouslytransmit heat in an in-plane direction rather than in a direction normalto the plane of the sheet. Thus, the graphitic carbon sheet transmitsheat that originates from a battery cell away from the outboard metalliclayer 38. In certain embodiments, the outboard metallic layer 38comprises a lightweight metal or metal alloy. Preferably, structurallayer 38 comprises aluminum, an aluminum alloy, carbon fiber, or asynthetic resin material. The laminate structure of side panels 28, 30permit light-weight, relatively low melting-point metals such asaluminum to be used to be used in the construction of battery modulehousing 12, which saves considerable weight, which can be a tremendousadvantage particularly when the battery modules 10 are being installedwithin a vehicle where weight is an important design consideration.

Composite panels 28, 30 define, at least in part, respective passageways44 within housing 12 that are configured to conduct a flow of ejecta andgas from a thermal event associated with one or more battery cellswithin housing 12 toward respective outlets 46 formed in the housing. Itis noted that the battery module 10 illustrated in the Figures utilizesbattery cells that are configured to fail in the direction of compositeside panels 28 and 30. Thus, housing 12 is configured with a passageway44 at each end of the stack of battery cells to conduct ejecta and gastowards a respective outlet 46. However, it is within the scope of thepresent invention for battery module 10 to utilize battery cells thatare configured to fail in only one direction, thus requiring the use ofonly one composite side panel 28, one passageway 44, and one outlet 46.

As illustrated, outlet 46 is formed in end panel 32 so that the hot gasand ejecta is conducted away from the various electrical componentscarried by end panel 34. Diaphragms 36 normally seal outlets 46 and areconfigured to open in response to the thermal event and permitcommunication between the passageway 44 and the exterior of housing 12.In certain embodiments, diaphragms 36 are formed from a synthetic resinfilm material such as silicone rubber, KAPTON (Polyimide), TEFLON &GORE-TEX (Polytetrafluoroethylene), and the like. However, it is alsowithin the scope of the present invention for other materials, such asthin metallic foils, to be used as diaphragm 36. In one aspect of theinvention, diaphragms 36 function as one-way valves that rupture underthe pressure of a thermal event occurring within module 10 but aresufficiently heat-resistant to avoid rupturing due to a thermal eventoccurring and being vented from an adjacent module in close proximitythereto. Thus, diaphragms 36 may also protect module 10 from externalhazards as well as help alleviate hazards that are internal to module10.

Turning now to FIGS. 4 and 5, battery module 10 comprises a plurality ofbattery cells 48. As illustrated, battery cells 48 comprise prismaticbattery cells, but it is within the scope of the present invention forother types of battery cells to be used with many of the featuresdisclosed and described herein. Generally, though, the prismatic batterycells are placed within a cell frame 50. A plurality of frames 50 arestacked together and fastened by inserting threaded rods 52 throughorifices 54 formed in respective corner sections 56 of each frame.Frames 50 are generally rigid and made from an inert material, such as asynthetic resin or thermoplastic plastic material. A preferred materialfrom which fames 50 can be constructed is acrylonitrile butadienestyrene (ABS), although any suitable thermoplastic material may be used.Once a desired number of cells 48 have been stacked together, and endplate 58 is attached and secured to rods 52 with nuts 60. However, otherdevices can be used to secure the stacks of cells together includingcables and bands.

Each battery cell 48 comprises at least two terminals 62, 64 extendingtherefrom (see, FIG. 6). As illustrated, one terminal extends fromopposite ends of the cell 48, although it is within the scope of thepresent invention for terminals 62, 64 to extend from the same end ofthe cell. The battery module assembly 10 comprises one or more busbars66 that are operable to connect the plurality of battery cells 48located within housing 12. Busbars 66 are preferably formed of anyconductive material, such as copper or aluminum, and comprise a slot 68that is configured to receive terminals 62, 64.

It is noted that passageways 44 can carry wiring and/or other electricalcomponents used by battery module assembly. Upon suffering a thermalevent, the flame, ejecta, and gases expelled from a battery cell 48 candamage wire insulation thereby exposing the bare wires of thesecomponents. As busbars generally face passageways 44, if the bare wiringand busbars were to come into contact, a short circuit could be createdthereby introducing further hazards, such as the triggering of anotherrunaway cell, into an already perilous situation. Thus, in certainembodiments of the present invention, one or more busbar shields 70 maybe installed over busbars 66 to at least partially cover the one orbusbars 66 and shield electrical components that are located outboard ofthe one or more busbars 66 and within passage 44 from contacting the oneor more busbars 66 during a thermal event associated with one or more ofthe battery cells 48. In certain embodiments, the busbar shields 70 areformed from a fire-resistant material, preferably an FR4-rated sheetmaterial, such as that described above and used with composite sidepanels 28, 30. Busbar shields 70 may also operate to block flamesescaping from one battery cell 48 from contacting adjacent batterycells.

FIGS. 6 and 7 illustrate in greater detail an exemplary battery cell 48that may be used with embodiments of the present invention. Aspreviously mentioned, however, it is within the scope of the presentinvention for other types and configurations of battery cells to be usedand the figures and their accompanying description should not be takenas limiting upon the scope of the invention in any way.

Battery cell 48 comprises an outer cell case 72 in which the contents ofthe battery cell, such as the cathode, anode, and electrolyte, arecontained. In certain embodiments, the cell case comprises a pouch thatis formed of a film material, such as a polymer/aluminum compositematerial that is hermetically sealed at least on one side. The cell case72 presents a pair of opposed, generally planar surfaces 74, 76. Incertain embodiments, surfaces 74, 76 make up the majority of the surfacearea of the cell case. These planar surfaces 74, 76 are interconnectedby opposed sidewall segment pairs 78, 80, 82, 84. Sidewall segments 78,80 extend parallel to the longitudinal axis of battery cell 48, andsidewall segments 82, 84 extend transverse to the longitudinal axis ofbattery cell 48. Some of the case material may extend beyond one or moreof the sidewall segments 78, 80, 82, 84 in the form of a flangestructure 86. Flange structure 86 is generally a byproduct of themanufacturing of cell case 72 and may be created when the film materialmaking up the cell case 72 is sealed. As illustrated, flange structure86 extends circumferentially around the perimeter of battery cell 48,although, this need not always be the case. In particular embodiments,terminals 62, 64 extend through portions of flange structure 86 and areat least partially covered thereby.

In preferred embodiments of the present invention, a compressive wrap 88is disposed around the cell case 72 in covering relationship to at leasta portion of planar surfaces 74, 76, and at least a portion of one ofsidewall segment pairs 78, 80, 82, 84. In particularly preferredembodiments, compressive wrap is comprised of two overlapping plies 88of a self-adhesive sheet material. In especially preferred embodiments,the sheet material is a fiberglass reinforced film that has an adhesiveapplied to one side thereof. However, it is within the scope of thepresent invention for the compressive wrap 88 to be comprised of asingle ply or of a plurality of plies, and for the adhesive to beseparately applied rather than be an integral part of the film materialmaking up the wrap. The compressive wrap 88, in whatever form it takes,is operable to constrain hoop stresses acting upon the cell case 72during thermal expansion of the cell 48. As indicated, it is commonduring normal operation of a lithium ion battery cell for heat to begenerated. This heat will tend to cause the contents within the cellcase 72, and the cell case itself, to expand. Uncontrolled expansion ofthe cell case 72 can lead to unpredictable failure of the cell case 72during an untoward thermal event within the cell 48. It is an aim ofcertain embodiments of the present invention to prevent unpredictablefailures of the cell case 72, so that venting of released flame, gas,and ejecta can be effectively managed by the other anti-propagationfeatures described herein. Thus, while in most embodiments of thepresent invention, the majority of the cell case 72 is covered withcompressive wrap 88, at least a portion of the cell case 72,particularly at least a portion of one of sidewall segments 78, 80, 82,84 is left uncovered so as to create at least one predetermined point ofcell case failure during a thermal event in the cell 48 through whichejecta and gas, and possibly flame, are released from the cell. Incertain embodiments, the at least one predetermined point of cell casefailure is located within the same sidewall segment through whichterminals 62 and 64 extend, namely sidewall segments 82 and 84.Preferably, the predetermined point of cell case failure 92 is locatedproximate the intersection of adjacent sidewall segments, and there isat least one predetermined point of cell case failure formed in each ofthe uncovered sidewall segments 82, 84. Thus, the compressive wrap 88 isconfigured to prevent failure of the cell case 72 at any location on thecell case that that is covered by compressive wrap 88 prior to failureat the at least one predetermined point of failure 92. In certainembodiments, the material making up the compressive wrap 88 has atensile strength of at least 2.5 MPa, and preferably from 2.5 to 10 MPa,from 3 to 9 MPa, from 4 to 8 MPa, or from 5 to 7 MPa. The materialmaking up the compressive wrap must maintain these mechanical propertieswhen exposed to heat sources in excess of 700° C., preferably acrossnormal operational temperatures of −40° C. to 60° C. and when exposed toheat sources of from 60° C. to 900° C.

Optionally, a protective wrap 90 may be applied over the top of thecompressive wrap 88. In certain embodiments, protective wrap 90comprises a heat-shrink plastic sleeve that is placed around batterycell 48. The sleeve is then heated to cause wrap 90 to shrink around thecell 48. Generally, protective wrap 90 may provide some additionalreinforcement for cell case 72. However, protective wrap 90,particularly when used with battery cell cases 72 that comprise aluminumcomposite films, provides a barrier for any exposed conductive cell casematerial to prevent corrosion or degradation thereof thereby helping tomaintain the structural integrity of the cell case, prevent the creationof unintended weak points therein that could become hazard concerns.

The present invention further comprises methods of constraining aprismatic battery cell 48 comprising cell case 72 in which the contentsof the battery cell are contained. The method comprises applyingcompressive wrap 88 to the cell case 72 in covering relationship to atleast a portion of planar surfaces 74, 76 and at least a portion of oneof the sidewall segment pairs 78, 80, 82, 84. At least one sidewallsegment is left uncovered by the compressive wrap thereby creating atleast one predetermined point of cell case failure 92.

In certain embodiments of the present invention, the battery cell 48comprises at least one pliable, temperature-resistant strip of material94 disposed on at least one side of and overlying the cell flange 86that surrounds each terminal 62, 64. Preferably, strip 94 comprises asilicone rubber material, but it may be formed from any pliable materialthat is capable of maintaining its structural integrity upon beingexposed to high temperatures, e.g., temperatures in excess of 300° C.Strip 94 may comprise a substantially uniform cross-sectional profile(i.e., presenting a uniform thickness), or it can be configured with avariable profile. As shown in FIG. 6, preferably strip 94 comprises acentral portion 98 that at least partially overlies terminals 62, 64 andoutboard portions 100, 102 that are laterally disposed from the centralportion. In addition, central portion 98 may have a thickness that isgreater than the thickness of outboard portions 100, 102. In certainembodiments, the thickness of central portion 98 is at least 1.5 timesthat of outboard portions 100, 102. Central portion 98 also need nothave a width that is as wide as the width of strip 94. As shown, raisedcentral portion 98 comprises a width that is less than the width ofstrip 94 so that an unraised segment 99 is located next to centralpotion 99 and intermediate to outboard portions 100, 102. In certainembodiments, unraised segment 99 has a thickness that is substantiallyequal to the thickness of outboard portions 100, 102. Also, centralportion 98 may also comprise a segment 101 that protrudes beyond themargin 103 of the outboard portions 100, 102. This segment 101 offersenhanced support for the portions of terminals 62, 64 that extend beyondcell flange 86.

In certain embodiments of the invention, the cell flange 86 extendsalong the entire length of one of the sidewall segments 82, 84 fromwhich at least one of the terminals 62, 64 extend. Strip 94 preferablyalso extends along the entire length of these sidewall segments.Preferably, strip 94 does not encroach upon or overlap cell case planarsurfaces 74, 76. Rather, strip 94 resides entirely outboard of themargins of these surfaces and outboard of the margins defining sidewallsegments 82, 84, although this need not always be the case.

In one aspect, as can be seen from FIG. 5, when a plurality of batterycells 48 are assembled into battery module assembly 10, strip 94 andcentral portion 98 in particular, provide support and mechanicalprotection for terminals 62, 64 and prevent physical damage thereto dueto motion or vibrations of the battery module assembly, such as whenbeing transported or installed within a vehicle. However, as explainedbelow, strip 94 may provide a secondary function, which is to directflames, ejecta, and gas upon being expelled through the predeterminedpoint of cell case failure 92 during a runaway thermal event and preventthese materials from spilling over onto an adjacent battery cell 48within module 10. In addition, strip 94 also provides protection forbattery cell 48, and in particular the sidewall segments 82, 84 fromwhich terminals 62, 64 extend, from flame, ejecta, and gas originatingexternal to the battery cell 48 to which it is applied. Thus, strip 94functions in certain respects as a one-way valve permitting gas, flameand ejecta originating within battery cell 48 to escape, but preventingthe same materials emitted from a different battery cell from entering.It has been discovered that when strip 94 comes into contact with, forexample, flames (or temperatures of approximately 700° C.) originatingoutside of battery cell 48, strip 94 is configured to char and notcombust. This charring of strip 94 insulates battery cell 48 and helpsto prevent propagation of thermal events originating outside of batterycell 48 from creating another hazardous thermal event within batterycell 48.

In certain embodiments, the point of cell case failure 92 is locatedinboard of strip 94 so that flames, ejecta, and gas that may be producedby cell 48 during a runaway thermal event are expelled from the cellbeneath the strip and not over the strip. Thus, strip 94 serves todirect these materials in a direction that is co-axial with thelongitudinal axis of the battery cell 48 and in a direction toward oneof the composite side panels 28, 30. Transmission of flames, ejecta, andgas laterally to an adjacent battery cell within the battery module 10is minimized or avoided completely.

Embodiments of the present invention also provide methods of protectingbattery cell 48 from physical and thermal damage by placing at least onepliable, temperature-resistant strip of material 94 as described above,on at least one side of and overlying the at least one cell flange 86surrounding each of terminals 62, 64.

In certain embodiments of the present invention, a layered barriermaterial 104 is provided as a part of the battery module assembly 10 tothermally isolate and control or prevent cell-to-cell propagation of athermal event occurring within at least one of the battery cells 48. Thelayered barrier material 104 is best viewed in FIG. 5. As illustrated,the barrier material 104 is posited in between cells 48 making upbattery module assembly 10. Preferably, the barrier material 104comprises at least two sheets of an anisotropic material 106, 107 havinga high thermal conductivity in the in-plane direction (as opposed to ina direction normal to the sheet). In preferred embodiments, theanisotropic material 106, 107 comprises graphitic carbon, and morepreferably graphite.

One of the sheets of anisotropic material 106 is in direct facingcontact with one battery cell 48. Preferably, the sheet of anisotropicmaterial 106 is sized to substantially cover the cell case planarsurface 74 when placed in direct contact therewith (or in contact withany wraps or films secured to the cell case as described above). Theother sheet of anisotropic material 107 is placed in direct facingcontact with another battery cell 48 that is adjacent to the firstbattery cell. Similarly, the other sheet of anisotropic material 107preferably is sized to substantially cover the cell case planar surface76 of the other battery cell 48 when placed in direct contact therewith.The anisotropic material 106, 107 is operable to direct thermal energyaway from the cell surfaces 74, 76 with which it is in contact.Preferably, the anisotropic material 106, 107 conducts a significantamount of the thermal energy away from the cell toward the peripheralmargins of the sheet 106, 107 as opposed to conducting the thermalenergy in a direction that is normal to the sheet 106, 107 and in adirection that is toward an adjacent cell 48. In addition, theanisotropic material 106, 107 may also be operable to prevent and/orretard penetration of a flame originating from the battery cell 48 withwhich it is in contact in a direction toward the other, adjacent batterycell. This flame-barrier characteristic helps to protect and preservethe functionality of the other layers making up the layered barriermaterial 104 as described below. The anisotropic heat conduction andflame barrier functions may be performed by a single material or aplurality of materials.

As illustrated, the layered barrier material 104 further comprises atleast two sheets of a thermal insulation material 108 having a highthermal resistance. It is noted, that in certain embodiments of theinvention, the thermal insulation material 108 is optional, or that onlyone sheet of thermal insulation material 108 may be used. Thus, thefollowing description should not be viewed as limiting upon the overallscope of the invention. In certain embodiments, the thermal insulationmaterial 108 does not provide meaningful structural support to thelayered barrier material 104 or any other portion of battery moduleassembly 10 and is fully pliable in response to forced acting upon it byother portions of the layered barrier material. The thermal insulationmaterial 108 maintains its insulating properties when exposed totemperatures in excess of 800° C. In certain embodiments, the thermalinsulation material 108 also remains dimensionally stable when exposedto heat and pressure. Particularly, this means that the thickness of thethermal insulation material does not substantially change when placedunder compressive forces or when subjected to temperature fluctuationsas might be experienced during normal battery operation or during athermal event. In preferred embodiments, the insulation materialcomprises cork, wool, or fiberglass. The thermal insulation material 108is operable to retard and/or impede the flow of heat energy originatingwithin one of the battery cells 48 in a direction toward at least oneother adjacent battery cell. It is noted that the heat energy beingimpeded can originate in the cell 48 that is located proximal or distalto the thermal insulation material 108. The same directionalfunctionality is also true of the sheets of anisotropic material 106,although, its most effective thermal barrier characteristics will beprovided for the cell 48 with which it is in contact.

One of the sheets of thermal insulation material 108 is positioned indirect facing contact with one of the sheets of anisotropic material106, and one other of the sheets of thermal insulation material 108 ispositioned in direct facing contact with one other of the sheets ofanisotropic material 106. Preferably, the sheets of thermal insulationmaterial 108 are sized to correspond with the sheets of anisotropicmaterial 106, particularly so that the sheet of anisotropic material 106substantially covers the sheet of thermal insulation material whenplaced in direct abutting contact therewith. In certain embodiments, thesheet of anisotropic material 106 may comprise slats 110 that extendtransversely from respective longitudinal side margins of the sheet.When placed in direct facing contact with the thermal insulationmaterial 108, slats 110 cover the longitudinal side margins of thethermal insulation material 108, thereby causing the thermal insulationmaterial 108 to “nest” within the sheet of anisotropic material 106.

The layered barrier material 104 further comprises a compliant material112 positioned between the at least two sheets of thermal insulationmaterial 108. Preferably, the compliant material 112 is undercompression when positioned between the sheets of thermal insulationmaterial 108 meaning that it is compressed and/or reduced in volume fromits natural or unconstrained state so that the internal forces actingwithin the compliant material 112 bias the material toward theunconstrained state. The compliant material 112 may be compressed, forexample, when the stack 49 of battery cells is assembled and endplates58 are secured to the ends of the stack by threaded rods 52 and nuts 60.As mentioned previously, other devices can be used to provide thiscompressive force such as bands or cables. In preferred embodiments, thecompliant material comprises a urethane, EPDM, PVC, or silicone foam.The compliant material 112 must exhibit high compressibility (down to25% of its original thickness) without a compression set. It mustcontinue to exert forces on the thermal insulation material andanisotropic material when exposed to temperatures in excess of 700° C.,preferably across normal operational temperatures of −40° C. to 60° C.and when exposed to heat sources of from 60° C. to 900° C. In certainaspects of the invention, the compliant material 112 is operable formaintaining the anisotropic material 106, 107 in direct facing contactwith the battery cells 48 regardless of thermally-induced changes involume that the battery cells may experience during normal celloperation. In addition, by being assembled in a compressed state, shouldthe compliant material 112 itself experience changes in volume due tochanges in temperature within the battery module assembly 10, theinternal forces within the compliant material acting in an outwarddirection remain sufficient to remove any gaps or air pockets that maytry to form in between battery cells 48 and sheets 106, 107. The slatsof anisotropic material 106 may also be configured to extend over andcover the longitudinal side margins of the compliant material 112 sothat the complaint material also nests within sheet 106.

Sheet of anisotropic material 107 may also be provided with slats 113that extend transversely from respective longitudinal side margins ofthe sheet. In certain embodiments, slats 113 are larger than slats 110,and are configured to extend at least partially over and cover sidewallsegments 78, 80 of battery cell 48. Sidewall segments 78, 80 may alsohave an elongate spacer 114 applied to at least a portion thereof. Whenthe battery cells 48 are stacked and assembled, spacer 114 is positionedin between sidewall segments 78, 80 and slats 113.

With reference to FIG. 2, it is noted that battery module housing 12 hasa longitudinal axis X-X that extends the length of the battery modulehousing and a transverse axis Y-Y that is normal to the longitudinalaxis. In certain embodiments of the present invention, battery moduleassembly 10 is configured so that a compressive force is placed on thebattery cells residing therein in directions parallel to both axes X-Xand Y-Y. As discussed above, the compressive forces in a directionparallel to axis X-X may be provided by the layers of compliant material112 that are interspersed among the various battery cells. Suchcompressive forces may be applied by other means as well, including thebanding of the cell stack 49 together. This compressive force maintainsthe sheets of anisotropic material 106, 107 in direct facing contactwith the battery cells 48 to ensure that thermal energy may be conductedaway from battery cells 48 by sheets 106, 107. Straps 20 are positionedaround battery module housing 12 and are configured to apply acompressive force to at least panels 14 and 16 in a direction that isparallel to axis Y-Y. It is noted that other structures may be used inlieu of straps 20 to supply a compressive force to panels 14, 16, andthe illustrated embodiment should not be viewed as limiting.

As can be seen in FIG. 3, this compressive force causes panels 14 and 16to remain in contact with slats 110 and/or 113 of the sheets ofanisotropic material 106, 107. Panels 14, 16, and possibly the entirebattery module housing, can be configured to function as a heat sink toconduct thermal energy away from battery cells 48 transmitted to it viathe sheets of anisotropic material 106, 107. In order to accomplish thiseffectively, slats 110 and/or 113 should remain in continuous directcontact with panels 14, 16. Thus, it is a feature of certain embodimentsof the present invention to compress the stack of battery cells in atleast two planes so that the sheets of anisotropic material remain incontinuous contact with battery cells 48 and panels 14, 16 of housing12. Accordingly, sheets of anisotropic material 106, 107 can be viewedas devices for conducting thermal energy away from battery cells 48 anddelivering it to the battery module housing 12.

The layered barrier material 104 does not need to be positionedintermediate all adjacent battery cells 48. In certain embodiments,there could be two, three, four, or any plurality of cells positioned inbetween each layer of layered barrier material 104. As illustrated inFIG. 5, the stack 49 of battery cells may be constructed of a pluralityof repeating battery cell units 116. Each unit comprises at least twocell frames 50, at least two battery cells 48, and at least one layeredbarrier material 104. Note, as illustrated in FIG. 5, cell frames 50 areoriented in mirrored format as opposed to facing the same direction.Between adjacent cell units 116 one or more sheets of anisotropicmaterial 107 may be placed. In preferred embodiments, sheets ofanisotropic material 106, 107 are oriented so that slats 110, 113 allextend in the same direction away from their respective sheets.

FIG. 8 illustrates another embodiment of the present invention. In thisembodiment, a stack 118 of battery cells 120 is assembled. The stack 118is similar in many respects to stack 49 described above, and for thesake of expediency, such commonalities are not restated in detail below,but are clear from the Figures. Like stack 49, stack 118 is adapted tobe placed within a battery module housing 12 like that described abovehaving housing panels 14, 16. Battery cells 120 are prismatic batterycells having a pair of terminals 121 extending from the same sidewallsegment and being at least partially surrounded by flange 86. Batterycells 120 are placed within cell frames 50 that are fastened together inthe form of a plurality of repeating battery cell units 122. Batterycell units 122 comprise at least two battery cells 120 having a layeredbarrier material 104 positioned therebetween. Layered barrier material104 may be configured as previous described above and comprise sheets ofanisotropic material 106, 107, optional sheets of thermal insulationmaterial 108, and at least one layer of a compliant material 112.

Each battery cell 120 further comprises a bead 124 of a pliable,temperature-resistant material disposed about a majority of theperiphery of the sidewall segments of the battery cell. The bead 124 maycomprise the same material use to construct pliable strips 94 describedabove. Bead 124 overlies at least a portion of the cell flange 86 and isoperable to apply a compressive force to the outer cell case, andparticularly the sidewall segments to constrain the sidewall segmentsand prevent rupture of the cell case at unintended points along thevarious sidewall segments. Bead 124 may be continuous (i.e., one pieceas is illustrated in FIG. 8) or discontinuous (i.e., made up of discretesegments) that are individually placed around cell 120. In certainembodiments, bead 124 may be provided with one or more recessed areas126 or areas of reduced thickness. Recessed areas 126 representcorrespond with predetermined points of cell case failure 92 wherecontrolled cell case rupture during a thermal event is to occur. Thus,preferably, bead 124 provides support and reinforcement for the majorityof the sidewall segment circumference, except for those portionscorresponding with recessed areas 126. It is noted that in the case of adiscontinuous bead, recessed areas 126 may actually be void of any beadmaterial.

In certain embodiments, battery cells 120 are not reinforced with acompressive wrap 88 as battery cells 48 may be. Thus, in addition toperforming the functions of vibration protection for terminals 121 and aflame barrier for preventing entry of flame originating external to cell120, bead 124 is configured to constrain the cell sidewalls by providinga compressive force thereto. This compressive force provided by bead 124reinforced the cell case and prevents cell case failure at locationsother than predetermined points 92.

Generally, battery cell stack 118 may be substituted for cell stack 49and placed within a battery module housing 12 configured as describedabove, and except as noted above, the operation of such a battery module10 remains the same as previously described.

Embodiments of the present invention also provide methods of thermallyisolating battery cells 48 within battery module assembly 10. The methodcomprises positioning layered barrier material 104 in between at leasttwo adjacent battery cells 48. The positioning of the layered barriermaterial 104 comprises placing a first sheet of the anisotropic material106 in direct facing contact with a first battery cell 46, placing afirst sheet of the thermal insulation material 108 in direct facingcontact with the first sheet of anisotropic material 106, placing asecond sheet of the anisotropic material 106 in direct facing contactwith a second battery cell, placing a second sheet of the thermalinsulation material 108 in direct facing contact with a the second sheetof anisotropic material 106, and positioning the compliant material 112between the first and second sheets of thermal insulation material 108.The compliant material 112 is maintained under compression between thefirst and second sheets of thermal insulation material 108.

Battery module assembly 10 can have a variety of applications. In apreferred application, a plurality of battery module assemblies 10 canbe provided in a stack or cabinet, and even a plurality of cabinets ofbattery module assemblies provided, to form a battery system. Thebattery module assembly 10 or a battery system comprising a plurality ofbattery module assemblies can be used to provide power to a vehicle,such as a car, truck, boat, aircraft, hyperloop pod, mining equipment,aviation ground service equipment, or locomotive. A preferredapplication for battery module assembly 10 is use within a batterysystem that is installed within a marine vessel. The marine vessel canbe a cargo ship, a passenger ship, a ferry, a hovercraft, a militarycraft, or the like. Moreover, the battery system comprising batterymodule assembly 10 may be the only power source provided on board themarine vessel, or it can be provided as one component of a hybrid powersystem. The battery system comprising battery module assembly 10 may beused to provide propulsion for the vehicle, to provide power for otheronboard vehicle systems, or both.

It is understood that the present invention can be practiced employingone or more of the various features and elements described herein. Thefact that the embodiments shown in the figures and described above showcombinations of elements assembled in a particular manner should not betaken as limiting on the scope of the present invention, nor should itbe taken as requiring all of said features or elements to be present inorder to successfully practice the present invention.

1. A prismatic battery cell comprising: an outer cell case in which thecontents of the battery cell are contained, the cell case presenting apair of opposed, generally planar surfaces interconnected by opposedsidewall segment pairs; a compressive wrap disposed around the cell casein covering relationship to at least a portion of the planar surfacesand at least a portion of one of the sidewall segment pairs, thecompressive wrap being operable to constrain hoop stresses acting uponthe cell case during thermal expansion of the cell, there being at leastone sidewall segment of one of the sidewall segment pairs that isuncovered by the compressive wrap and configured to create at least onepredetermined point of cell case failure during a thermal event in thecell through which ejecta and gas are released from the cell.
 2. Theprismatic battery cell of claim 1, wherein the compressive wrap preventsfailure of the cell case at any location on the cell case that iscovered by the compressive wrap prior to failure at the at least onepredetermined point.
 3. The prismatic battery cell of claim 1, whereincompressive wrap comprises a tensile strength of at least 2.5 MPa. 4.The prismatic battery cell of claim 1, wherein the compressive wrapcomprises a self-adhesive fiberglass reinforced film.
 5. The prismaticbattery cell of claim 1, wherein the at least one predetermined point ofcell case failure is located at the intersection of two adjacentsidewall segments.
 6. The prismatic battery cell of claim 1, whereinthere are two sidewall segments of one of the sidewall segment pairsthat are uncovered by the compressive wrap, there being at least onepredetermined point of cell case failure formed in each of the side wallsegments of the one of the sidewall segment pairs.
 7. The prismaticbattery cell of claim 1, wherein the battery cell is a lithium ionbattery cell.
 8. A method of constraining a prismatic battery cellcomprising a cell case in which the contents of the battery cell arecontained, the cell case presenting a pair of opposed, generally planarsurfaces interconnected by opposed sidewall segment pairs, the methodcomprising: applying a compressive wrap to the cell case in coveringrelationship to at least a portion of the planar surfaces and a least aportion of one of the sidewall segment pairs, the compressive wrapfunctioning to constrain hoop stresses acting upon the cell case duringthermal expansion of the cell, leaving at least one sidewall segment ofone of the sidewall segment pairs uncovered by the compressive wrapthereby creating at least one predetermined point of cell case failureduring a thermal event in the cell through which ejecta and gas arereleased from the cell.
 9. The method of claim 8, wherein thecompressive wrap is a fiberglass reinforced film that is adhered to thecell case.
 10. The method of claim 8, wherein the compressive wrapprevents failure of the cell case at any location on the cell case thatis covered by the compressive wrap prior to failure at the predeterminedpoint.
 11. The method of claim 8, wherein the at least one predeterminedpoint of cell case failure is located at the intersection of twoadjacent sidewall segments.
 12. The method of claim 8, wherein there aretwo sidewall segments of one of the sidewall segment pairs that are leftuncovered by the compressive wrap, there being at least onepredetermined point of cell case failure formed in each of the side wallsegments of the one of the sidewall segment pairs.
 13. The method ofclaim 8, wherein the battery cell is a lithium ion battery cell. 14.-54.(canceled)
 55. A battery module assembly comprising: (1) a batterymodule housing configured to house a plurality of prismatic batterycells, one or more of the prismatic battery cells comprising: (i) anouter cell case in which the contents of the battery cell are contained,the cell case presenting a pair of opposed, generally planar surfacesinterconnected by opposed sidewall segment pairs; (ii) a compressivewrap disposed around the cell case in covering relationship to at leasta portion of the planar surfaces and at least a portion of one of thesidewall segment pairs, the compressive wrap being operable to constrainhoop stresses acting upon the cell case during thermal expansion of thecell, there being at least one sidewall segment of one of the sidewallsegment pairs that is uncovered by the compressive wrap and configuredto create at least one predetermined point of cell case failure during athermal event in the cell through which ejecta and gas are released fromthe cell; and (2) a layered barrier material disposed in between atleast two of the plurality of prismatic battery cells, the layeredbarrier material configured to thermally isolate and control or preventcell-to-cell propagation of a thermal event occurring within at leastone of the battery cells, the layered barrier material comprising— (i)at least two sheets of an anisotropic material, at least one of thesheets of anisotropic material being in direct facing contact with oneof the at least two battery cells, and at least one other of the sheetsof anisotropic material being in direct facing contact with one other ofthe at least two battery cells; (ii) optionally at least two sheets of athermal insulation material, one of the at least two sheets of thermalinsulation material being positioned in direct facing contact with oneof the at least two sheets of anisotropic material, and the other of theat least two sheets of thermal insulation material being positioned indirect facing contact with the other of the at least two sheets ofanisotropic material; and (iii) a compliant material positioned betweenthe at least two sheets of thermal insulation material undercompression, the compliant material being operable for maintaining theat least two sheets of anisotropic material in direct facing contactwith the at least two battery cells. 56-67. (canceled)
 68. The batterymodule assembly of claim 55, wherein the battery module housingcomprises at least one composite panel comprising an outboard metallicor non-metallic structural layer, an inboard layer of an FR4-rated sheetmaterial, and at least one graphitic carbon sheet positionedtherebetween, wherein the composite panel defines at least in part apassageway configured to conduct a flow of ejecta and gas from a thermalevent associated with one or more battery cells within the batterymodule housing toward an outlet formed in the housing.
 69. The batterymodule assembly of claim 68, wherein the housing further comprises atleast one side panel positioned transversely relative to the compositepanel, the outlet being formed in the at least one side panel, andwherein the outlet is normally covered with a rupturable diaphragmconfigured to open in response to the thermal event and permitcommunication between the passageway and the exterior of the housing.70-74. (canceled)
 75. The battery module assembly of claim 68, whereinthe battery module assembly further comprises one or more busbarsoperable to connect the plurality of battery cells located within thehousing, and wherein the battery module assembly further comprises oneor more busbar shields configured to at least partially cover the one ormore busbars and shield electrical components located outboard of theone or more busbars and within the passage from contacting the one ormore busbars during a thermal event associated with one or more of theplurality of battery cells. 76-78. (canceled)
 79. The battery moduleassembly of claim 55, wherein each of the plurality of battery cellscomprises at least one cell flange extending from one or more of thesidewall segments, at least two terminals extend from one or more of thesidewall segments, the at least two terminals being at least partiallysurrounded by the at least one cell flange, there being at least onepliable, temperature-resistant strip of material disposed on at leastone side of and overlying the at least one cell flange. 80-91.(canceled)
 92. A vehicle comprising a prismatic battery cell accordingto claim
 1. 93-95. (canceled)